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Mathematica

Radius in FindClusters

Al Guy

Posted 10 years ago

How can I cluster the list so that elements that are within specified distance or less from each other gather together in the sublist? Thanks. t = RandomInteger[1000, 50]; FindClusters[ t, DistanceFunction -> ManhattanDistance] Matbe some other functionlike `SplitBy` or `GatherBy` should be used, but how to insert the condition on the radius (two cases - one with the specified region in which to gather elements, and another with specified maximum distance from one another) ?

POSTED BY: Al Guy

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Henrik Schachner

Henrik Schachner, Radiation Therapy Center, Weilheim, Germany

Posted 10 years ago

Hi Al Guy, I do not have an other idea than using brute force: Increasing the number of clusters, until the desired result is reached. ClearAll["Global`"] maxElemDist[clusters_List] := Max[(Differences /@ (Sort /@ clusters)) /. {} -> Sequence[]] t = RandomInteger[1000, 50]; ( the goal, e.g.: ) elemDistLimit = 20; numberOfClusters = 1; While[elemDistLimit <= maxElemDist[clusters = FindClusters[t, numberOfClusters]], numberOfClusters++] ( result: ) clusters ( lets check: *) maxElemDist[clusters] Maybe this already helps. Regards -- Henrik

Hi Al Guy,

I do not have an other idea than using brute force: Increasing the number of clusters, until the desired result is reached.

ClearAll["Global`*"]

maxElemDist[clusters_List] := Max[(Differences /@ (Sort /@ clusters)) /. {} -> Sequence[]]

t = RandomInteger[1000, 50];
(* the goal, e.g.: *)
elemDistLimit = 20; 

numberOfClusters = 1;
While[elemDistLimit <= maxElemDist[clusters = FindClusters[t, numberOfClusters]],
 numberOfClusters++]

(* result: *)
clusters

(* lets check: *)
maxElemDist[clusters]

Maybe this already helps.

Regards -- Henrik

POSTED BY: Henrik Schachner

Al Guy

Posted 10 years ago

I see. Actually `Gather` is supposed to do the job but it doesn't: t = {17, 9, 29, 23, 1, 32, 14, 21, 11, 24, 2, 7, 31, 16, 22, 5, 3, 18, 20, 25, 30, 26, 12, 8, 15, 13, 27, 19, 4, 10, 6, 28}; Gather[t, (Abs[#1 - #2] <= 1) &] In this case the should all line up in one sublist. They don't. Why?